Fatty esters are widely used commercially in a variety of applications. Commonly used esters include natural fats and oils, especially triglyceride oils. Well known examples include soybean oil, canola oil, olive oil, linseed oil, and tung oil.
Another important type of fatty ester is biodiesel, a clean-burning alternative fuel produced from domestic, renewable resources. Biodiesel contains no petroleum, but it can be blended at any level with petroleum diesel to create a fuel blend. It can be used in compression-ignition (diesel) engines with little or no modification. Biodiesel is biodegradable, essentially nontoxic, and essentially free of sulfur and aromatic compounds, and thus can provide certain environmental advantages.
Biodiesel is essentially a mixture of methyl, ethyl, and/or isopropyl esters of fatty acids, made through transesterification of fatty acid triglycerides (oils) with the respective alcohols. The most commonly used raw material oils are seed oils such as soybean oil, palm oil, and rapeseed oil.
These and many naturally occurring fats and oils contain a component, sometimes a major one, of unsaturated fatty acids (mainly in the form of esters). These include such acids as oleic, linoleic, linolenic, and others bearing one or more olefinic moieties. Accordingly, biodiesel fuels made from these oils also typically contain unsaturated acids and/or esters thereof. In both natural oils and biodiesel, the unsaturation makes the materials susceptible to oxidation by atmospheric oxygen. Such oxidation, for example during processing or storage, may result in an increase in viscosity and/or pour point temperature, which in many cases is undesirable. Therefore, ways of reducing or eliminating oxidative degradation of fatty esters are sought in the various industries in which these materials are used.